(i) Field of the Invention
The present invention relates to an apparatus for forming a film and a method for forming the film, and more specifically, it relates to an apparatus for forming a film by applying the film on the surface of a substrate and then drying this film, and a method for forming the film.
(ii) Description of the Related Art
In the coating of a photoresist film used in a photolithography technique, a spin coater can usually be used. The spin coater spins a substrate after a coating solution has been fed onto the surface of the substrate, and from the coating solution spread all over the surface of the substrate by this spin, the photoresist film can be formed. The thus obtained photoresist film can be applied onto the surface of a substrate such as the glass substrate of a liquid crystal display, a printed circuit board, a semiconductor substrate, the glass substrate of a photomask or a ceramic substrate for use in the manufacture of a thermal head. This photoresist film can be subjected to various treatments such as a drying treatment, an exposure treatment, a developing treatment and a washing treatment to form a pattern such as a conductive pattern or an insulating pattern on the surface of the substrate.
With the enlargement of liquid crystal displays, the size of substrates has also increased, but this increase in size has been to the intent that it is difficult to form the photoresist film by the spinning treatment using the spin coater. Consequently, in recent years, a film applicator called a slit coater has been developed. The slit coater has a slit nozzle which can move within a specific width on the surface of the substrate, and this slit coater can apply the photoresist film within the specific width on the surface of the substrate while moving. In short, the slit coater is characterized by being able to apply the photoresist film having a desired film thickness at one action.
In general, the photoresist film applied by the slit coater is in a wet state, and the substrate with this wet film can then be delivered to a vacuum drying device in a next step, in which the photoresist film can be dried under the low pressure conditions in this low pressure drying device. For the delivery of the substrate from the slit coater to the low pressure drying device, a robot can be used for the purpose of automatic delivery, and in this case, the substrate can be gripped by a hand of the robot and then delivered.
The photoresist film applied by the slit coater is in the wet state, so that the hand of the robot comes in contact with the wet photoresist film formed on the substrate. A trace of the hand remains on the photoresist film, or the thickness of the photoresist film alters owing to a difference of temperature between both the members. The damage of the photoresist film which is brought about at the time of the delivery by the robot can be previously avoided by forming a holding region on the surface of the substrate.
In the case where a rectangular substrate, having the length of its one side is in the range of 200 to 700 mm, is used as the glass substrate of the liquid crystal display, and in the case where the above-mentioned slit coater is used, a photoresist film-free region having a width of 2 to 5 m from the edge toward the center of the substrate surface is required to remain along the periphery of the substrate surface. This region is the holding region in which the substrate can be gripped by the hand of the robot.
However, there has been a tendency for a substrate such as the glass substrate which can be used in the above-mentioned liquid crystal display to be enlarged, and the effective region in which the pattern can actually be formed on the surface of the substrate by the photolithography technique is required to be as large as possible. However, the formation of the above-mentioned holding region makes the acquisition of a sufficiently effective area impossible. If the holding region is limited, the handling of the substrate by the hand of the robot is difficult and some restriction is put on the handling of the substrate at the time of delivery. Thus the delivery of the substrate cannot be carried out smoothly, with the result that the productivity of the substrates deteriorates disadvantageously.
Furthermore, the substrate on which the wet photoresist film has been applied by the slit coater is delivered to the low pressure drying device in the next step by the robot as the substrate delivery device. Therefore, the slit coater and the low pressure drying device are separately installed on a substrate treatment plant line, and this fact disadvantageously results in the enlargement of the substrate treatment plant line.